Threaded closure system for medical liquid container

ABSTRACT

A medical liquid bottle having a threaded neck of one thermoplastic material is blow-molded at pressures of 50 to 150 psi (3.52 to 10.1 kg/cm2) so there is a low amount of internal stress in the neck. A cap of a different thermoplastic material is injection molded at pressures of 5,000 to 20,000 psi (352 to 1,410 kg/cm2) producing a very high internal stress in this cap. After liquid has been placed in the bottle and the cap assembled to the neck, the bottle with the combined cap and neck are stress relieved by subjecting to steam sterilization at 240* to 260* F. (116* to 127* C.). This causes the cap to shrink more than the neck and to form a bacteria-tight thermoplastic-to-thermoplastic hermetic seal. Despite this very tight hermetic seal the closure is openable with an unexpectedly low unscrewing torque of 10 to 30 inch-pounds (11.5 to 34.5 centimeter-kilograms) manually applied by a nurse or physician.

Dec. 2, 1975 THREADED CLOSURE SYSTEM FOR MEDICAL LIQUID CONTAINERAssignee:

Filed:

Inventors: Elmer F. St. Amand, North Hollywood; Thomas R. Thornbury, LaCrescenta, both of Calif.

American Hospital Supply Corporation, Evanston, Ill.

Mar. 7, 1973 Appl. No.: 338,684

US. Cl. 128/272; 215/246 Int. Cl. A61j l/00 Field of Search 128/272;206/47 R; 215/43,

References Cited UNITED STATES PATENTS Primary E.\'aminerRichard A.Gaudet Assistant Examiner-J. C. McGowan Attorney, Agent, or FirmLarry N.Barger; Robert T. Merrick [57] ABSTRACT A medical liquid bottle having athreaded neck of one thermoplastic material is blow-molded at pressuresof 50 to 150 psi (3.52 to 10.1 kg/cm so there is a low amount ofinternal stress in the neck. A cap of a different thermoplastic materialis injection molded at pressures of 5,000 to 20,000 psi (352 to 1,410kg/cm producing a very high internal stress in this cap. After liquidhas been placed in the bottle and the cap assembled to the neck, thebottle with the combined cap and neck are stress relieved by subjectingto steam sterilization at 240 to 260 F. (116 to 127 C.). This causes thecap to shrink more than the neck and to form a bacteria-tightthermoplastic-tothermoplastic hermetic seal. Despite this very tighthermetic seal the closure is openable with an unexpectedly lowunscrewing torque of 10 to 30 inchpounds (11.5 to 34.5centimeter-kilograms) manually applied by a nurse or physician.

4 Claims, 6 Drawing Figures U.S. Patent Dec. 2, 1975 Sheet 1 of 23,923,062

US. Patent Dec. 2, 1975 Sheet 2 of 2 3,923,062

flm cyce 7) (ECU/14 75MB) THREADED CLOSURE SYSTEM FOR MEDICAL LIQUIDCONTAINER BACKGROUND Sterile medical liquids are frequently supplied bymanufacturers to hospitals in sterilized bottles. One type of bottleused for the medical liquids is termed a pouring container. Thiscontainer has a wide mouth of approximately 1 inch (2.54 cm) diameter.Thus a physician can quickly pour the sterile liquid into a surgicalwound for a flushing action.

An extremely critical area of these pouring containers is the closuresystem. The closure must reliably maintain the sterile nature of theliquid in the bottle and also be easy to open.

In the past, pouring containers included glass type bottles with doubleclosures. The double closure had an inner metal screw cap with aresilient liner or gasket engaging the glass bottle. An outer closuresecured over the inner screw cap formed an additional sterility barrier.One of the problems with such a closure was that thegasket of the innerscrew cap would not always compress to the same extent. This caused someclosures to be very difficult to manually unscrew. One can readilyappreciate such a problem by considering the difficulty of opening someglass food jars with metal screw caps and gaskets.

SUMMARY OF THE INVENTION This invention overcomes the problems mentionedabove by providing a unique structure and process that eliminates theneed for a separate resilient sealing gasket. In this invention a bottlehas an integrally formed externally threaded thermoplastic neck. Boththe bottle and neck are formed of a thermoplastic material blowmolded atpressures of 50 to 150 psi (3.52 to 10.1 kg/cm) to cause low internalstresses to be molded in the neck. An internally threaded screw cap of adifferent thermoplastic material is injection molded at pressures of5,000 to 20,000 psi (352 to 1,410 kglcm to create very high internalstresses in the screw cap. After liquid contents have been placed in thebottle, and the screw cap threaded onto the neck, this assembly isheated preferably by steam sterilization to 240 to 260 F. (1 16 to 127C.). This causes a substantially greater amount of stress relief in thecap than in the neck. When this happens the rigid cap shrinks more thanthe rigid neck to provide a thermoplastic-tthermoplastic bacteria-tighthermetic seal of increased tightness between the cap and neck.

It would be expected that such a seal would be too tight to openmanually. Shrink film sleeves previously used to secure corks or plugsin wine bottles have gripped so tightly that they had to be cut apartwith a knife. In the present invention it has unexpectedly been foundthat the very tight hermetic seal can be opened with approximately 20inch-pounds (23 centimeterkilograms) of unscrewing torque. A nurse orphysician can readily apply this amount of torque manually.

THE DRAWINGS FIG. 1 is an exploded partially cut away view of the innerscrew cap and bottle neck combination;

FIG. 2 is an enlarged fragmentary sectional view of the inner and outerclosure system prior to opening; and

FIGS. 3 through 6 show the bottle and closure system at various steps inthe method of forming and opening the improved closure system.

DETAILED DESCRIPTION In FIG. 1 a thermoplastic bottle 1 is shown havingan integral dispensing neck 2. This neck has an external flange 3 andexternal threads 4. The container is partially filled with sterilemedical liquid 5. At a base of the container is a flexible hanging tab'6secured in a recess at the bottom of the bottle. This hanging tab 6 canbe snapped out of the recess for suspending the bottle neck downwardlywhen dispensing the liquid through an irrigation set or the like.

FIG. 1 shows the bottle neck 2 that is integrally formed with thebottle. Both the bottle neck and bottle are blow-molded of apropylene-ethylene copolymer. This blow-molding takes place'at pressuresof 50 to psi (3.52 to 10.1 kglcm to create low internal stresses in thethermoplastic bottle neck.

Shown directly above the bottle neck in FIG. 1 is an inner screw capclosure 7, with a top wall 8 and a depending skirt 9. This cap is formedof a second thermoplastic material that is different from the firstthermoplastic material of the threaded neck. Cap 7 is injection moldedat pressures of 5,000 to 20,000 psi (352 to 1,410 kg/cm to create a highamount of internal stress in the cap 7.

As mentioned above the thermoplastic material of the bottle and neck isdifferent from the thermoplastic material of the cap. For example, thebottle neck has been made of a propylene-ethylene copolymer and whencooled to room temperature after blow-molding, this copolymer shrinks ata rate of 0.009 to 0.020 inch/- linear inch (0.009 to 0.020centimeter/linear centimeter). The cap 7 is of a high densitypolyethylene that shrinks when cooled to room temperature after moldingat a rate of 0.020 to 0.050 inch/linear inch (0.020 to 0.050centimeter/linear centimeter). After these two materials shrink from themold, they still contain internal stresses. These post molding stressesare substantially greater in the cap than in the bottle neck. Thedifferent amount of stresses can readily be seen under polarized light.

There are many conditions that contribute to molded in stresses inthermoplastic materials. These can be mixing times, moldingtemperatures, cooling times, etc. However one of the main reasons formolded in internal stresses is the pressure at which the molten plasticis forced into a mold. In the blow-molded bottle and neck the pressureis very low, such as 50 to 150 psi (3.52 to 10.1 kglcm This is believedto result in the low amount of internal stresses in the thermoplasticneck. The cap is injection molded at very high pressures of from 5,000to 20,000 psi (352 to 1,410 kglcm This is believed to be the reason forthe large amount of molded in internal stresses. Both the bottle neckand cap are molded at approximately 400F. (205C).

Normally the molded-in stresses are undesirable and much effort is madeto eliminate them. However, in this invention these undesirable stresseshave been used to create an improved thermoplastic-to-thermoplasticseal.

These stresses are preferably formed in the cap by injection molding theinternally threaded cap of FIG. 1 with a top wall and a longitudinaldepending skirt. Preferably the cap is molded with an injection gatelocated in a central portion of the top wall in an area such as theposition of numeral 8 in FIG. 1. This is so the stresses will radiateoutwardly from such injection gate and then downwardly longitudinallyalong the skirt. When such a cap is relieved of its molded in stressesit will tend to shrink along the stress lines and cause the top todiametrically shrink and the skirt to longitudinally shorten.

After cooling to room temperature, liquid is placed in the bottle andthe cap assembled to the neck. This unit then is heated such as by steamsterilization to a temperature of 240 to 260 F. (116 to 127 C.) and thensubsequently cooled to room temperature. During the heating orsterilization cycle there is substantially more stress in the cap thanin the bottle neck that is relieved. This causes the cap to shrink morethan the neck and tightly grip the bottle neck.

A more detailed illustration of the cap structure is shown in theenlarged sectional view of FIG. 2. As shown in FIG. 2, the inner screwcap closure 7 is threadingly received on the bottle neck 2. Preferablythere is an integral compressible thermoplastic rib 11 on the cap thatengages a top lip surface 12 of the thermoplastic bottle neck. Thishelps to make a tight hermetic seal between the screw cap and bottleneck. The outer closure structure includes a cap 13 with a frangiblebrim 14 that is fused to flange 3. This provides an enclosed encasementfor the inner cap 7. A threaded jacking ring 15 has threads 16 thatintermesh with external threads 17 of the outer cap 13. This jackingring fractures the frangible brim to open the outer closure. The jackingring and its operation is more fully explained in a copendingapplication by Pradip V. Choksi and Roy B. Steidley, filed March 7,1973, Ser. No. 338,662.

In FIGS. 3 to 6 the sequence of forming and opening the container isshown with the outer closure of FIG. 5 partially cut away for clarity.In FIG. 3 the thermoplastic container of propylene-ethylene copolymercontains a medical liquid, such as 5% dextrose, normal saline, water,etc. Next, in FIG. 4 the thermoplastic inner closure is placed on thethreaded neck and screwed down against the bottle neck. The innerclosure can be removed at this stage in the process at a torque of5inch-pounds (5.7 centimeter-kilograms) to 20 inch-pounds (23centimeter-kilograms). After the inner closure has been so assembled,the outer closure is sealed to the container as shown in FIG. 5. Thenthe container with both closures as shown in FIG. 5 is subjected to heator steam sterilization at 240 to 260 F. (116 to 127 C.) and maintainedat this temperature for approximately 5 minutes. Thereafter, the entirecontainer and closure system and the liquid therein are cooled to roomtemperature. It has been found that this process creates an improvedsea] at lip surface 12 between the rigid threaded high densitypolyethylene screw cap and the rigid threaded neck of the bottle. Apropylene-ethylene copolymer marketed by Eastman Chemical Company underthe trademark TENITE works very well for the bottle and neck.

A shrink fit closure that improves the sealing characteristics of athermoplastic-to-thermoplastic hermetic seal (without the use of aseparate sliding gasket) would normally be expected to tighten down somuch that it would be difficult to remove the inner screw cap. Shrinkbands of thermoplastic film used for forming a secondary seal on winebottles and the like grip the bottle and closure so tightly that theshrink bands have to be cut apart to open the bottle.

It has been unexpectedly found that the disclosed screw cap and bottleneck structure of this invention does not have the removable problem ofprevious shrink bands, such as used on wine bottles. While the hermeticseal of applicants invention is improved with the differential shrinkagebetween the high density polyethylene screw cap and thepropylene-ethylene c0- polymer bottle neck, it simultaneously provides aclosure with a relatively constant opening torque of approximately 20inch-pounds (23 centimeterkilograms). In actual practice this openingtorque does not extend beyond the range of 10 to 30 inch-pounds (11.5 to34.5 centimeter-kilograms). Therefore the differential shrinkage both:(1) tightens the hermetic seal and (2) adjusts the opening torque ofeach closure.

The release torque required to remove the caps from the bottles wasfound to be very consistent after sterilizing, regardless of the initialtorque used to seal the cap. Consequently, with a cap that was initiallyput on with a torque of 5 inch-pounds (5.7 centimeter-kilograms), theremoval torque was 20 inch-pounds (23 centimeter-kilograms). A cap thatwas initially put on with a torque of 20 inch-pounds (23centimeter-kilograms) also came off at 20 inch-pounds (23centimeterkilograms). This relatively constant opening torque is easilyapplied with a hand twisting motion by the nurse or physician.

In the foregoing specification a specific embodiment has been used todescribe this invention. However, it is understood by those skilled inthe art that certain modifications can be made to these embodimentswithout departing from the spirit and scope of the invention.

We claim:

1. A container with a threaded closure screwed onto a threaded neckforming a unit with inner and outer members, wherein the improvement isthat the neck and closure are of different thermoplastic materialsformed with substantially different internal stresses, said threadedclosure and threaded neck being in a state of post-assembly stressrelief with substantially greater amounts of shrink in the outer membercausing the threaded neck and threaded closure to grippingly engage eachother with increased tightness at a thermoplastic-to-thermoplasticbacteria-tight hermetic seal, and there is a deformable thermoplasticrib at the hermetic seal, which closure is openable with a manuallyapplied unscrewing torque despite the tight hermetic seal.

2. The combination of claim 1, wherein the deformable thermoplastic ribis an integral portion of the closure.

3. A container with a threaded closure screwed onto a threaded neckforming a unit with inner and outer members, wherein the improvement isthat the neck and closure are of different thermoplastic materialsformed with substantially different internal stresses, said threadedclosure and threaded neck being in a state of post-assembly stressrelief with substantially greater amounts of shrink in the outer membercausing the threaded neck and threaded closure to grippingly engage eachother with increased tightness at a thermoplastic-to-thermoplasticbacteria-tight hermetic seal, and the outer member is an internallythreaded cap with a transverse wall having a centrally locatedinjecthreaded skirt connected with the wall, said wall and skirt beingintegrally formed with the cap so that the thermoplastic cap developsstresses radiating outwardly from a center portion of the wall and thenlongitudinally along the skirt, whereby the stress relief diametricallycontracts the wall and longitudinally shortens the cap skirt, whichclosure is openable with a manually applied unscrewing torque despitethe tight hermetic seal.

4. For storing, transporting and handling sterile medical liquid, thecombination of: a thermoplastic bottle with an integral externallythreaded neck of a propylene-ethylene copolymer blow-molded at pressuresof from 50 to 150 psi. to create a low amount of internal stresses; asterile medical liquid within the bottle; and internally threaded capformed of a high density polyethylene injection molded at pressures offrom 5,000 to 20,000 psi. to create a high amount of internal stresses;an integral compressible rib on the cap forming an annular contact withthe bottle neck; said threaded cap and threaded neck being in a state ofpost-assembly stress relief with a substantially greater amount ofshrink in the threaded closure causing it to grippingly engage the neckwith increased tightness at a thermoplastic-to-thermoplasticbacteria-tight hermetic seal at the rib, which closure is openable witha manually applied unscrewing torque of 10 to 30 inch-pounds despite thetight hermetic seal.

1. A container with a threaded closure screwed onto a threaded neckforming a unit with inner and outer members, wherein the improvement isthat the neck and closure are of different thermoplastic materialsformed with substantially different internal stresses, said threadedclosure and threaded neck being in a state of post-assembly stressrelief with substantially greater amounts of shrink in the outer membercausing the threaded neck and threaded closure to grippingly engage eachother with increased tightness at a thermoplastic-tothermoplasticbacteria-tight hermetic seal, and there is a deformable thermoplasticrib at the hermetic seal, which closure is openable with a manuallyapplied unscrewing torque despite the tight hermetic seal.
 2. Thecombination of claim 1, wherein the deformable thermoplastic rib is anintegral portion of the closure.
 3. A container with a threaded closurescrewed onto a threaded neck forming a unit with inner and outermembers, wherein the improvement is that the neck and closure are ofdifferent thermoplastic materials formed with substantially differentinternal stresses, said threaded closure and threaded neck being in astate of post-assembly stress relief with substantially greater amountsof shrink in the outer member causing the threaded neck and threadedclosure to grippingly engage each other with increased tightness at athermoplastic-to-thermoplastic bacteria-tight hermetic seal, and theouter member is an internally threaded cap with a transverse wall havinga centrally located injection molding gate and a longitudinal internallythreaded skirt connected with the wall, said wall and skirt beingintegrally formed with the cap so that the thermoplastic cap developsstresses radiating outwardly from a center portion of the wall and thenlongitudinally along the skirt, whereby the stress relief diametrIcallycontracts the wall and longitudinally shortens the cap skirt, whichclosure is openable with a manually applied unscrewing torque despitethe tight hermetic seal.
 4. For storing, transporting and handlingsterile medical liquid, the combination of: a thermoplastic bottle withan integral externally threaded neck of a propylene-ethylene copolymerblow-molded at pressures of from 50 to 150 psi. to create a low amountof internal stresses; a sterile medical liquid within the bottle; andinternally threaded cap formed of a high density polyethylene injectionmolded at pressures of from 5,000 to 20,000 psi. to create a high amountof internal stresses; an integral compressible rib on the cap forming anannular contact with the bottle neck; said threaded cap and threadedneck being in a state of post-assembly stress relief with asubstantially greater amount of shrink in the threaded closure causingit to grippingly engage the neck with increased tightness at athermoplastic-to-thermoplastic bacteria-tight hermetic seal at the rib,which closure is openable with a manually applied unscrewing torque of10 to 30 inch-pounds despite the tight hermetic seal.